I just finished cobbling together an R12K O2. Most of it came from a R10K O2 that was destroyed in shipping, but I managed to fix some of it. I added memory from a donor O2 (The original memory was physically broken), and an R12K from eBay.

It works great! My only problem is that it should have 1GB of RAM, but I can't seem to get it to find it all. I've rearranged, swapped memory with known-working machines, etc. with no luck. I would have thought that with pairs required, it would never be just 128MB short. 896MB is fine, but would like to figure out what's wrong!

The reason I ask is because my O2 has a problem with 128MB kits with memory modules with chips only one one side of the module. The modules with chips on both sides work fine and don't give any errors.

The modules with chips on one side did't register properly and they caused random memory errors, which went away when I removed them.

What can be a bit misleading about this kind of 128MB memory kit (single-sided), is that each module say's 128Mb on it, when in-fact the modules are only 64MB each, to make up the 128MB kit! So you end up thinking that you have 256MB, when in-fact you only have 128MB!

The 128mb kit shown here consists of two 64mb modules, but what can be misleading about them is the fact that each of them has 128 on it, but of you take a close look, you will notice the 01/128 KIT of 2 and 02/128 KIT of 2

I currently have four double sided 128mb modules installed in the machine, which work perfectly.

It's always seems like a good idea to give machine it's full compliment of ram, but in truth, you only really need as much ram as the machine actually uses, and for what I use mine for, the 512mb that I currently have installed is more than enough.

Many machines of the era, not only SGIs, have problems with higher-density modules.Some don't. That's why you see sometimes "official ceiling 512MB, unofficial tested 1024MB" in machines from the era. That means the machine had no trouble with higher-density chips.

The double-sided ones, as it seems to me, are the lower density ones, therefore more compatible. More chips to reach the final capacity of the stick.Apologies if I'm stating the obvious (given our audience), or saying something totally stupid.

AFAIK, all O2s officially supported 1 GB of RAM. My old group received its first batch of O2s as soon as they were shipping commercially in 1996, and they were sold as supporting 1 GB. (Ours shipped with 128 MB or 256 MB, but they all ended up with 1 GB after a few years.)

My guess is either RAM modules are faulty or the slots are faulty. Also check that the slots and the modules are clean and free of dust.

I happen to have two such memory kit's and even when I only had them slotted into the first and second memory banks in the machine, it gave me sporadic memory issues.

I don't think that the memory slots in the machine themselves are defective, as they work perfectly fine with the SGI branded double sided 128mb memory modules that I have, but I just think that it's strange that the two single-sided kits that I acquired from different places seem to give me the same problem.

It's a pity that I don't have an extra O2 with a different motherboard revision to test with at the moment. (A perfect excuse to maybe acquire another one in the future I suppose )

I have asked Ian Mapleson in the past, what the difference between the various O2 motherboard revisions was, especially the rare and expensive 030-1327-001 and 030-1327-002 and he said that he didn't know and that the price was simply dictated due to rarity. Maybe some motherboard revisions just had better RAM support. (ie single sided ram from Kingston for example.)

Fair enough. I'm still skeptical that it's a motherboard version issue, though, since it seems like it would be very common knowledge by now if there were O2 motherboards that had distinctive RAM requirements.

Then again, I seem to be getting old enough now that I keep forgetting what I've forgotten.

I've seen O2's (and Octanes) that had problems with memory sticks, but I've never been able to pin it on the sticks themselves. I had the feeling it affected the memory sockets furthest away from the CPU, so might be related to signal integrity. No amount of cleaning would fix it.

For the Octane mainboard there's also the locking mechanism of the XIO connectors which gets really close to the soldering pins of some of the DIMM sockets.

To accentuate the special identity of the IRIS 4D/70, Silicon Graphics' designers selected a new color palette. The machine's coating blends dark grey, raspberry and beige colors into a pleasing harmony. (IRIS 4D/70 Superworkstation Technical Report)